The present disclosure relates generally to gasification systems, and more specifically, to a gasifier that includes an integral preheater fuel and moderator injection system. Such a gasifier can be integrated in an integrated gasification combined cycle (IGCC) power generation system or any other chemical processing system.
At least some known combined cycle power systems used for power generation include a gasification system that is integrated with at least one power-producing turbine system. For example, known gasifiers convert a mixture of fuel, air or oxygen, steam, and/or limestone into an output of partially combusted gas, sometimes referred to as “syngas.” Hot combustion gases produced are supplied to the combustor of a gas turbine engine, which powers a generator that supplies electrical power to a power grid. Exhaust from at least some known gas turbine engines is routed to a heat recovery steam generator that generates steam for driving a steam turbine. Power generated by the steam turbine also provides additional electrical power to the power grid.
Gasifiers tend to be physically large devices that typically must be preheated prior to the initiation of the actual gasification process. Preheating a gasifier may take several hours, due to the size and bulk of a typical gasifier. In at least some known gasifiers, the preheater structures, including injectors or nozzles for fuel and oxidizer, are removable components that must be inserted into the gasifier shell prior to preheating, and then removed following preheating. After removing the components, the gasification feedstock feed structures used during the actual gasification process must be installed, aligned, secured and checked for leaks, amongst other procedures, before the actual gasification process can begin. Preheater structures operate using gaseous fuels, such as natural gas or propane. However, the gasifier feedstock feed structures that deliver fuels such as pulverized coal, are ill-suited to deliver natural gas, propane, or other gaseous or atomizable liquid agents.
The removal of the preheater structures, and subsequent installation of the gasification feed structures can take several hours. During this time, the interior of the gasifier can begin to cool down. Accordingly, because the refractory materials lining the interior of the gasifier must be at a minimum “light-off” temperature before the gasification process can begin, it may be necessary to preheat the interior of the gasifier to a higher temperature and/or for a longer period of time, in order to accommodate the loss of heat and temperature that occurs during the changeover of preheater and gasification feed equipment. Furthermore, plant workers may be compelled to hurry their work in order to complete the installation of the gasification feedstock injection equipment before the gasifier has cooled too much. The equipment used in both the preheater and gasification feedstock feed structures tend to be large, heavy, and cumbersome and awkward to handle. Accordingly, each switchover between preheater and gasification structures involves safety issues resulting from the nature of the equipment being moved, and the perceived sense of urgency of the crews performing the equipment switchover.
In at least some other known gasification systems, preheater structures are provided in gasifiers that are permanently installed. However, such preheater structures are operated continuously, including during actual gasification. Continued operation of such equipment can result in premature degradation of the preheater structures due to thermal cycling. Accordingly, it would be desirable to provide a system and method for preheating a gasifier in a plant that addresses the foregoing efficiency, safety and equipment degradation concerns.